CMV, a β-herpes virus, is a frequent and ubiquitous virus that affects all populations, worldwide, including adults and children with normal or compromised immune systems. CMV replication in the immunosuppressed host, if left unchecked, results in severe morbidity, mortality and other complications such as predisposition to bacterial and fungal infections, graft versus host disease and potential graft failure. CMV infection is the most common infection in patients undergoing hematopoietic stem cell transplantation (HCT) or solid organ transplantation (SOT). CMV is prevalent in 50-80% adult transplant candidates and found at lower prevalence in children. The current Gold Standard (Valganciclovir, Ganciclovir) is myelotoxic, and interferes with bone marrow engraftment in HCT. Therefore, its use in this population is limited to pre-emptive therapy, and the duration of its administration and the size of dose are often limited by its toxicity. This toxicity also limits the duration of prophylactic use and the dose in SOT. As a result, a new agent without the toxicities of Valganciclovir, Ganciclovir that allows for more effective prevention of CMV disease and transplant engraftment, and that substantially reduces treatment-related complications would represent a major break-through.